1. Field of the Invention
The present invention relates to a liquid crystal display system and more particularly, a liquid crystal display device having a matrix array of switching transistors connected to reflective electrodes, which are addressable row by row.
2. Description of the Prior Art
A reflective-type liquid crystal display device has been known which comprises a matrix array substrate, a transparent insulating substrate provided with a transparent common electrode, and a liquid crystal layer sandwiched between the two substrates. The matrix array substrate is arranged such that a plurality of field effect transistors (FET) or thin film transistors (TFT) are formed as switching elements on a semiconductor or insulator substrate. An output terminal of each transistor is coupled to a reflective pixel electrode across an insulating layer of silicon oxide, silicon nitride, or the like. For example, some of such conventional devices are disclosed in U.S. Pat. 4,103,297 and in a report "High density reflective type TFT array for high definition liquid crystal projection TV system" by Y. Takubo et al., in SID 1989 Japan Display, pp. 584-587.
The operation of the reflective-type liquid crystal display device having the foregoing arrangement will now be described.
When a gate drive signal for selecting pixels is fed to the gate electrode, the transistor becomes activated and thus, an image signal is transmitted from the source electrode of the transistor to the reflective pixel electrode. As the result, a voltage is applied to the liquid crystal between the reflective pixel electrode and the opposite common electrode for image development. At the time, an incident light which comes through the opposite transparent substrate is reflected on the reflective pixel electrode. Also, portions of the light are polarized during transmission across the liquid crystal layer so that a contrast appears between polarizing pixels and not-polarizing pixels to form an image. Black stripes are also provided for defining a boundary between two adjacent pixels and thus, ensuring improvements in the picture quality.
However, the conventional device is fabricated in particular by forming an insulating layer over the switching elements, providing contact holes in the insulating layer and thereafter, forming the reflective pixel electrodes, so that its process becomes complicated with a large number of masks. Accordingly, the cost of production will disadvantageously be increased.